It is well known that individuals who are confined to wheelchairs or stationary chairs for extended periods of time are susceptible to the development of ischaemie or decubitus ulcers on their buttocks and thighs, particularly in areas where only small amounts of tissue separate bony structure from the surface of the skin. These ulcers are caused by a lack of circulation of blood in the lower extremities, and by prolonged pressure on thin tissue areas. Many months of treatment, and quite often surgery, are required to heal these ulcerations, to say nothing of the pain, the expense and the complete loss of productivity of the patient, with no assurance that the condition will not recur.
Many devices and appliances have been developed to provide relief to individuals who suffer from these ulcers.
Pernell, in U.S. Pat. No. 3,158,878, discloses a foam cushion with cut-out areas in the zones most susceptible to ulceration, and Green, In U.S. Pat. No. 4,132,228, discloses a contoured and relieved cushion. Trenchard, in U.S. Pat. No. 3,721,232, discloses a surgical pad filled with gelatinous compound, and Graves et al, in U.S. Pat. No. 3,858,379, teaches a process for making such a pad, while Panaia et al, in U.S. Pat. No. 4,493,488, discloses a varied density pad, and its installation in a conventional folding wheelchair. These cushions and pads, while providing greater comfort to a seated patient, do nothing to enhance the circulation of blood in the critical areas.
Other devices and mechanisms have addressed the problem of sustained pressure on the buttocks area, as in the case of a seated person, and over the entire body, as in the case of a person confined to a bed on a long term basis. Some of these devices and mechanisms are disclosed in U.S. Pat. Nos. 1,643,793, 2,122,702, 2,445,158, 2,448,777, 2,684,672, 2,906,259, 3,464,406, 3,467,081, 4,267,610, 4,280,487 and 4,494,260. It is noted that many of these prior art devices are cumbersome and complex, comprising a multiplicity of cams and cam followers, gears, levers, pumps, valves and compressors, rendering the apparatus unsuitable for application to a conventional wheelchair or stationary chair that is used by most handicapped persons.
Kubicek, in U.S. Pat. No. 3,050,050, discloses an alternating pressure seat comprising vertically movable slats, while Dahl, in U.S. Pat. No. 3,970,077, utilizing similar mechanisms, substitutes the use of vertically moving blocks. Schulman, in U.S. Pat. No. 4,524,762, discloses a similar device actuated by a fluid inflatable bag. More recently, Joiner, in U.S. Pat. No. 4,574,901, discloses a method of removing pressure from the buttocks of a seated individual by periodically lowering the rear section of the seat.
Tsuda et al, in U.S. Pat. No. 4,155,592, discloses a seat having a backrest provided with a plurality of belts extending transversely thereof, and electrically driven tensioning means for successively tensioning the belts to change the contour of the padding means, which provides lumbar support or massages the back of the user.
While all these examples of the prior art may provide some beneficial and/or therapeutic effect to the patient, none have directly addressed or solved the problem which is the principal causal factor in the development of decubitus ulcers, namely, lack of nourishment of body tissue, created by an insufficient supply of blood to areas where only small amounts of tissue separate bony structure from the surface of the skin, and the prolonged continuous pressure of the patient's weight upon these areas.
It is an object of this invention to provide a method for improving the blood circulation of a person seated in a chair by providing a flexible supporting surface, which flexible surface is alternately tensioned and relaxed from the front to the rear of the seat in an undulating motion, thereby stimulating the circulation of blood from the lower extremities, while, at the same time, changing the points of pressure exerted by the seat on the thighs and buttocks of the person seated in the chair.
Another object is to provide a seat for handicapped persons or persons who must remain inactive in a seated position for extended periods of time, which seat comprises a flexible surface of transversely extending straps, which produce an undulating, wave-like motion to the thighs and buttocks, and provides an action similar to that of a "progressing cavity" pump, to raise venous blood from the lower extremities and push it passed the thighs, buttocks and gluteal region, while periodically relieving the pressure imposed on those areas by the patient's weight, and allowing the blood flow to nourish and cleanse the tissue in these areas.